BatchedMesh Instance and Geometry Deletion Issue

Based on your description, you've identified what appears to be a potential issue with the BatchedMesh implementation in Three.js. Let me clarify what's happening:

The Issue

You're encountering a problem when:

1. Adding geometries to a BatchedMesh
2. Creating instances of those geometries
3. Deleting instances
4. Attempting to delete geometries that no longer have active instances

The error occurs because deleteGeometry is trying to validate instance IDs that were already "deleted" (marked as inactive).

How BatchedMesh Deletion Works

From your analysis of the code, you're correct that:

• deleteInstance() only sets the active property to false on the instance info entry
• This "soft deletion" approach doesn't fully remove the instance from internal tracking
• When deleteGeometry() is called, it doesn't properly account for these inactive instances

Potential Workaround

Since this appears to be a limitation in the current implementation, you might need to implement a workaround:

1. Keep your own tracking of which instances belong to which geometries
2. Before deleting a geometry, manually check if it has any active instances
3. If you need to delete a geometry, you might need to handle the instance cleanup yourself

Example Approach

JAVASCRIPTCopied
// Custom tracking
const geometryToInstances = new Map();

// When creating instances, track them
function createInstance(geometryId, ...) {
    const instanceId = batchedMesh.addInstance(...);
    
    if (!geometryToInstances.has(geometryId)) {
        geometryToInstances.set(geometryId, new Set());
    }
    geometryToInstances.get(geometryId).add(instanceId);
    
    return instanceId;
}

// When deleting instances, update tracking
function deleteInstance(geometryId, instanceId) {
    batchedMesh.deleteInstance(instanceId);
    
    const instances = geometryToInstances.get(geometryId);
    if (instances) {
        instances.delete(instanceId);
        
        // If no more instances, clean up the geometry
        if (instances.size === 0) {
            // Custom geometry cleanup logic here
            geometryToInstances.delete(geometryId);
        }
    }
}

This issue does seem like it could be a bug or limitation in the current BatchedMesh implementation. The behavior you've observed suggests that the internal tracking of instances and geometries might need improvement to handle dynamic deletion scenarios better.